N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
Chemistry
Unit 5: Gases, Liquids, Solids
Clarifying Statements
May, 2006
In this unit, students will study the characteristics of the common phases of
matter; namely solids, liquids, and gases. In order to effectively investigate these
characteristics, the students must have a basic understanding of the kinetic
molecular theory. This theory explains the properties of matter in terms of the
“energy of the particles and the forces that act between the particles”. (Modern
Chemistry HRW, p 303). By the end of this unit, students will be able to compare
and contrast the states of matter in terms of kinetic energy, general properties
(such as surface tension of liquids and diffusion of gases), and attractive forces
between molecules (intermolecular forces).
Gases
The kinetic-molecular theory, as it is applied to ideal gases, accounts for the
following properties: expansion, low density, compressibility, diffusion, effusion,
and fluidity (Modern Chemistry HRW, p. 304-305). Students must be able to
identify, describe, and explain these properties of gases.
Students must recognize the “variables that influence the behavior of gases”
(TEKS 7) such as pressure, temperature, volume, and number of particles.
Students should know that barometers and manometers are used to measure
pressure in millimeters of mercury and that atmospheres, torrs, and pascals are
also units of pressure.
Student should understand the relationship between the temperature scales of
Kelvin and Celsius. This relationship is based on the fact that absolute zero, the
lowest possible temperature, is equivalent to 0 Kelvin or –273C. Students should
also understand that the term standard temperature and pressure (STP)
describes a system at 0C and 1 atm. This information is important as it will be
used by students in future calculations.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
Chemistry
Unit 5: Gases, Liquids, Solids
Clarifying Statements
May, 2006
Students must also understand how gas laws are mathematical models of the
following relationships: pressure and volume (Boyle’s Law), volume and temperature
(Charles’s Law), and pressure and temperature (Gay-Lussac’s Law). The following
graphs are representations of these relationships.
Dalton’s law of partial pressure enables scientists to accurately measure gases by
water displacement. Students must be able to use this law in order to calculate
pressure of a gas collected over water.
Students must also be able to use the combined gas law to calculate the effect of
varying the conditions of a gas.
The ideal gas law establishes the relationship between pressure, volume,
temperature, and the number of moles of a gas. Students must be able to use the
ideal gas law in order to calculate property values of a gas at STP.
Liquids
The kinetic-molecular theory, as it is applied to liquids, accounts for the following
properties: fluidity, indefinite shape, definite volume, high density, ability to
diffuse, relative incompressibility, and surface tension (Modern Chemistry HRW, p.
363-364).
Solids
The kinetic-molecular theory, as applied to solids, accounts for the following
properties: definite shape, definite volume, definite melting point, very high
density, incompressibility, and very low rate of diffusion. (Modern Chemistry HRW,
p. 368-369).
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
2
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
Chemistry
Unit 5: Gases, Liquids, Solids
Clarifying Statements
May, 2006
Phase Changes
At this point, students should be able to compare and contrast the general
properties of solids and liquids. They should also be familiar with phase change
terms such as evaporation, condensation, sublimation, etc. As matter changes
states, it either absorbs or releases heat energy. Students must know that heat is
absorbed as a solid becomes a liquid, as well as when a liquid becomes a gas.
Conversely, they should also know that heat is released when a gas becomes a liquid
and when a liquid becomes a solid. If time permits, teachers may wish to study
equilibrium and Le Chatelier’s principle in order to further explain the energy
changes that occur as matter changes state.
Students must be able interpret phase diagrams (such as the following), that
depict the effect of pressure and temperature on phase states. They should also
be able to understand the significance of the triple point and critical point.
Finally, students must be able to explain the concept of equilibrium vapor
pressure; and be able to describe boiling, freezing, and melting in terms of kinetic
energy, temperature, and pressure.
Throughout this unit, students will have many opportunities to analyze data tables
and graphs. Students will also continue to strengthen their measuring techniques
and general lab skills, as well as improve their knowledge of significant figures and
the metric system.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for instructional
design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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